Nuclear magnetic resonance (NMR) spectroscopy is an analytical tool used by chemists and physicists to study the properties of atoms and molecules. NMR spectroscopy exploits the fact that the nuclei of some atoms are spin-active, meaning they possess a magnetic moment and can be aligned with an external magnetic field. By applying a radiofrequency (RF) pulse of the correct frequency, the spins can be induced to flip from their low-energy state (aligned with the magnetic field) to a higher-energy state (anti-aligned with the magnetic field). The energy of the RF pulse is absorbed by the nucleus, and this energy is converted into rotational energy, which can be detected and used to obtain information about the atom or molecule.
NMR spectroscopy is usually performed in either a liquid or gas state, but it can also be performed in the solid state. In liquids, the nuclei are free to move about, and the resulting NMR spectra are typically broad and complex. In gases, the nuclei are much more constrained, and the resulting NMR spectra are typically narrower and simpler. Solid-state NMR spectroscopy is a special case, where the nuclei are confined to their lattice sites and the resulting spectra are very narrow and highly structured.
2D NMR spectroscopy is a powerful technique that can be used to obtain detailed information about the structure and dynamics of molecules. In 2D NMR spectroscopy, two RF pulses are applied, with the second RF pulse applied at a different frequency from the first. This creates a two-dimensional spectrum, with the first dimension corresponding to the frequency of the first RF pulse and the second dimension corresponding to the frequency of the second RF pulse. The 2D NMR spectrum can be used to obtain information about the structure of the molecule, as well as the dynamics of the molecule on the nanosecond to millisecond time scale.
2D NMR spectroscopy is a powerful tool for the study of small molecules and proteins. In many cases, 2D NMR spectroscopy can provide information that cannot be obtained by any other technique. For example, 2D NMR spectroscopy can be used to study the structure of proteins in solution, as well as the dynamics of proteins on the nanosecond to millisecond time scale. 2D NMR spectroscopy can also be used to study the structure of small molecules in solution, as well as the dynamics of small molecules on the picosecond to nanosecond time scale.